Advice after your nerve block for surgery
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Introduction
We have given you this factsheet because you have an appointment for a CT colonography scan. Please make sure you read this information and follow the instructions carefully before your procedure. If you have any further questions, please speak to a member of your healthcare team who will be pleased to advise you.
The procedure involves a computerised tomography (CT) scanner taking images of your abdomen and pelvis. These images are cross-sectional (like slices) and are used to produce 2D and 3D images of the large bowel (colon) to look for polyps or tumours.
This information may not answer all your questions, and it is not meant to replace informed discussion between you and your doctor but can act as a starting point for such discussions. If you have any questions about the procedure, please ask the doctor who has referred you or the department that will be performing it.
Are there alternatives to CT Colonography?
Colonoscopy is an alternative way of examining the large bowel. In this, a thin tube with a camera on the end (colonoscope) is passed into the back passage and moved up and around the bowel. The procedure is more invasive than CT colonography and usually requires sedation. However, it does allow a biopsy (tissue removed for testing) or polyp removal if needed.
Colonoscopy will only examine the inside of the large bowel. CT colonography also provides some information about other organs and structures inside the abdomen.
Preparation for the procedure
To give us a clear view, you must follow some dietary instructions before the test and taking a ‘tagging’ liquid called Omnipaque. Omnipaque is an iodine-based liquid which acts as a dye to help us distinguish stool from polyps.
You will need to follow instructions regarding the Omnipaque, and your diet, or the test may fail and may need repeating. These instructions are at the end of this booklet.
You will need to:
- drink the Omnipaque we have provided.
- follow a low fibre and low-fat diet.
Omnipaque may cause loose bowel movements, so it is important that you drink plenty of fluids to avoid becoming dehydrated. Please make sure you have access to and are near a toilet once you have started taking your bowel preparation.
Before your appointment (and before taking the Omnipaque)
Please let us know if:
- you suffer with an allergy to iodine or x-ray contrast.
- you have limited mobility and will require assistance to get on and off the scanner.
- you will need an interpreter. We are not able to use family members or friends to interpret.
- there is any possibility that you may be pregnant.
On Arrival
Please arrive 15 minutes before your scan time.
On arrival in the department, you should check in at the reception desk. Bring this letter with you and be prepared to confirm your details with the receptionist. All patients from 12-55 years of age (regardless of gender) who will undergo a Radiology procedure will be asked about the possibility of them being pregnant.
The procedure
- A Radiographer or Health Care Professional will call you from the waiting room for your CT scan. As other patients are having different scans and tests whilst you wait, you may note other patients being called out of order of arrival.
- Your scan may need some preparation beforehand. You may be asked to change into a hospital gown and remove jewellery (this may be best left at home, as the Trust cannot accept responsibility for lost or stolen items).
- We will explain the test, go through a checklist of questions and answer any questions you may have.
- We want to involve you in decisions about your care and treatment, and the test will only be performed if you consent to it. The radiographer/radiologist who will be performing your scan will ask you if you are happy for the procedure to go ahead - this is called verbal consent. If you do not wish to have the scan or are undecided, please tell the radiographer/radiologist. It is your decision and you can change your mind at any time.
- We will ask you to change into a hospital gown.
- A small needle (cannula) will be placed into your arm, in preparation for your scan.
- We may give you a muscle relaxant (Buscopan) via the cannula to prevent bowel spasm. This may give you a dry mouth and blurred vision for about 20 minutes.
- We will ask you to lie down on the scanner table on your left side.
- We will then pass a small, flexible tube into your anus (back passage) using lubricant gel.
- Carbon dioxide gas will be gently pumped into your bowel through the tube in your back passage from a specially designed machine. You may feel some bloating and mild discomfort in your abdomen like ‘trapped wind’.
- We will take CT scan pictures of you lying on your back, your front and/or your side. Sometimes we may take CT scan pictures of your chest to complete the examination.
- We will usually give you an infusion of x-ray contrast (dye) through the cannula in your arm. A short, hot flush and feeling like you are passing urine (weeing) are common side effects of this contrast.
- We will ask you to hold your breath for about ten seconds each time we take scan pictures.
- When we have completed taking images, the tube will be removed from your back passage
- We will then show you to the toilet. You may spend as long as you like in the toilet, until you feel more comfortable.
- You will then be able to get dressed.
- We will remove the cannula
- The procedure takes around 30 minutes, but please expect to be with us for an hour or so in total.
After the procedure
We will ask you to wait in the department for a short time after the procedure. This is to make sure that you feel well, and any abdominal discomfort is getting better before you go home.
You may experience some wind and further diarrhoea for the rest of the day. We recommend that you stay close to a toilet. You can eat normally after the procedure, and you should drink plenty of fluids.
Please seek urgent medical advice (your GP 9-5 or Accident and Emergency out of hours) if you experience any of the following symptoms over the next 4 days.
- Severe abdominal pain
- Increasingly painful abdominal discomfort
- Sweating and nausea
- Feeling generally unwell
You may have been given an injection, (Buscopan), used to relax the muscles in the bowel wall, during your examination. Blurring of your vision can be a side effect of this injection, although, this side effect is short lived, usually about 30 minutes. If you do experience this blurring, please make sure your vision has returned to normal before driving. You are advised to seek medical help if you develop painful blurred vision within 48 hours of this test as it may have brought out an underlying condition called Glaucoma.
Results
You will not receive the results of the investigation immediately as the images need to be carefully analysed. A specialist doctor (radiologist) or radiographer will write a report, and this will be sent to your consultant or specialist screening practitioner. This can take up to 4 weeks.
Risks
- There is exposure to X-ray radiation during the procedure. However, the amount of radiation you will receive is kept to as low as reasonably possible.
- Some people may have a rare allergic reaction to the x-ray contrast. We will go through a safety checklist before the procedure to identify if you are at increased risk. A hot flush, feeling of passing urine and metallic taste are common side effects of the x-ray contrast.
- No test is always 100% accurate and both CT colonography and colonoscopy can miss bowel tumours
Other side effects that may occur include:
- Painful, blurred vision of one or both of your eyes. This is a rare side effect from the muscle relaxant (Buscopan). If you experience this, you must attend hospital immediately.
- Abdominal discomfort. This should get better as you move around and start to eat.
- Damage to the bowel wall. This happens in less than 1 in 3000 tests. Most perforations of the bowel wall will resolve without any treatment, although overnight hospital admission and antibiotics under the care of a surgeon may be required.
- Dehydration. You should drink more fluids particularly during the bowel preparation.
- A sore bottom from loose stools.
If you have diabetes
If you are diabetic and need additional advice on how to manage your diabetic medication during the two days of preparation, please contact your diabetic nurse specialist or GP surgery for specific instructions.
| Day | Time | Diet, Drink, Medication | Completed Check |
| 7 Days before day of procedure | Stop any Iron supplements. Continue other medication | ||
| 4 days before procedure | Stop any constipating medication such as Loperamide. Continue other medication | ||
| 1 day before procedure |
Drink plenty of fluids |
||
| BEFORE BREAKFAST | Drink 1st dose of 50ml Omnipaque liquid. This can be mixed with water and squash to taste | ||
| 7am-9am |
Breakfast from the ‘low residue’ list |
||
| Clear Fluids only from now on – see below | |||
| BEFORE LUNCH | Drink 2nd dose of 50ml Omnipaque liquid. This can be mixed with water and squash to taste | ||
| 12-1:30pm |
Small light lunch from the ‘low residue’ list |
||
| No more solid foods, milk or dairy products. Clear Fluids only from now on – see below | |||
| 5-6pm | Drink 3rd dose of 50ml Omnipaque liquid. This can be mixed with water and squash to taste | ||
| 7-9pm | Supper. No solid foods allowed Clear soup or meat extract may be taken followed by clear jelly |
||
| Day of procedure | No solid foods, milk or dairy products. Continue with clear fluids | ||
| After Procedure | Eat and drink as normal | ||
Low Residue food examples
Eggs: Boiled, Poached
Cereal: Crisped rice cereal, corn flakes. No Bran or high fibre
Cheese: Cream cheese, cottage cheese, cheese sauce
Potatoes (no skin): Boiled, mashed, baked
Rice: plain boiled white rice
Pasta or noodles: White
Meat/Fish: lean beef, lamb, ham, pork, veal, poultry, fish
Bread: White
Desert: clear jelly
Clear Fluids: Water, energy drinks, soda water, black tea/coffee, squashes, strained fruit juice, clear soups or drinks made from stock/meat extract cubes
Contact us
If you have any queries relating to this information, please contact the Radiology service.
About this information
Service:
Radiology
Reference:
PILS-CT.16
Approval date:
25 March 2026
Review date:
25 March 2027
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Important note
This page provides general information only. It is developed by clinical staff and is reviewed regularly every 3 years for accuracy. For personal advice about your health, or if you have any concerns, please speak to your doctor.